I saw Jeff Ishaq's book, my copy just got delivered. It's a good read and very practical.

Here is another one from palmOne/peachpit this time:
http://www.amazon.com/exec/obidos/tg...bosnation0e-20

I see on Amazon that Jeff has another book due out in the spring:
Treo Essentials
http://www.amazon.com/exec/obidos/tg...bosnation0e-20